Method and apparatus for continuous mixing of liquids

ABSTRACT

Apparatus and method for mixing of a feed liquid with a process liquid comprising a pipe having a cylindrical bore, said process liquid flowing in the pipe, a throat in the bore, the portion of the bore downstream of the throat and forming an angle between said portion and the axis of said bore of up to about 15*, at least one feed nozzle for injection of said feed liquid disposed in said pipe and extending between a source of feed liquid and the bore, the nozzle opening into the bore at the throat and being cylindrical in cross section, the axis of the nozzle forming a second angle with a portion of the axis of the bore upstream of the nozzle, the second angle being from 30*-90* whereby said feed liquid is injected at a velocity of from 2 to 15 times the velocity of the process liquid.

United States Patent inventors Appl. No. Filed Patented Assignee Priority METHOD AND APPARATUS FOR CONTINUOUS MIXING OF LIQUIDS 12 Claims, 1 Drawing Fig.

U.S.Cl 239/4l6.2, 210/199, 239/117, 239/430 Int. Cl B051) 7/12 Field of Search 239/4162, 416.5, 429, 430, 431, 433, 434, 434.5; 210/198,

Primary Examiner-M. Henson Wood, Jr.

Assisjgr t Examiner-Michael Y. Mar

Artorney-Marmorek & Bierman and Ernest F. Marmorek, Jordan B. Bierman ABSTRACT: Apparatus and method for mixing of a feed liquid with a process liquid comprising a pipe having a cylindrical bore, said process liquid flowing in the pipe, a throat in the bore, the portion of the bore downstream of the throat and forming an angle between said portion and the axis of said bore of up to about 15, at least one feed nozzle for injection of said feed liquid disposed in said pipe and extending between a source of feed liquid and the bore, the nozzle opening into the bore at the throat and being cylindrical in cross section, the axis of the nozzle forming a second angle with a portion of the axis of the bore upstream of the nozzle, the second angle being from 30-90 whereby said feed liquid is injected at a velocity of from 2 to 15 times the velocity of the process liquid.

METHOD AND APPARATUS FOR CONTINUOUS MIXING OF LIQUIDS The present invention is directed to an improved mixing device, more specifically, to a mixing device intended for use in situations in which precise control of the ratio of liquids is required and wherein turbulent flow is not feasible.

Jet mixers for mixing of two or more liquid phases have been known in the art. However, they all suffer from certain very important deficiencies.

More specifically, in the case of the mixing of viscous liquids, their effect is impaired if not entirely eliminated. This is especially true if it is not feasible or possible to increase the velocities of the flowing liquids sufficiently to cause turbulent flow.

Orifice and whirl mixers are also known in the art. These devices contain various inserts in the mixing tube which cause repeated deflection or velocity change of the liquids flowing. By virtue of causing these changes, the desired mixing is obtained. However, these devices often form stagnant zones wherein no appreciable mixing takes place. Furthermore, their capacity is quite limited due to the necessity to have certain fixed flow cross sections. In injector mixers (also known in the art) the second liquid component or feed liquid is drawn into the main process liquid stream by passing it through a plurality of feed nozzles. These nozzles cause jet stream and develop the desired mixing. However, only a slight mixing effect is obtained as the orifices tend to clog and cleaning is difiicult. Furthermore, where viscous liquids are being used, the amount of actual mixing is minimized.

In an attempt to overcome these problems, a mechanical continuous mixer has been devised. In this apparatus, the feed liquid is introduced into the process liquid stream through a fairly wide opening. Immediately downstream of the opening, a mechanical mixer (such as a propeller) is installed and caused to rotate. This type of device suffers from the same deficiencies as the orifices and whirl mixers. These devices operate on fixed flow cross sections and consequently if the ratio of feed liquid to process liquid is to vary then the mixing effect will vary with the relative velocities.

It is well known that mixing under conditions of turbulent flow is relatively easy to carry out. However, there are many situations in which the two liquids must be thoroughly and completely mixed in the virtual absence of any turbulence.

. One very common such situation is when the liquids are 'of high viscosity. In order to obtain turbulent flow with such liquids it is necessary to increase the velocities to a point which is not commercially feasible or desirable. One specific process in which this problem arises is in the carrying out of the Beckmann rearrangement of cyclic ketoximes in the presence of sulfuric acid or phosphoric or polyphosphoric acids. This is accomplished by adding the oxime and the acid to the cycling reaction product at different points in the cycle. in the past this has been done through nozzles using a continuous flow mixer of mechanical type at each point. The flow mixers are provided with external drive installed in the circulating line.

When carrying out such mixing on a commercial scale problems arise particularly in the addition of the oxime to the cycling rearrangement mixture. The necessary thorough and uniform mixing leaves much to be desired. For example, at the feed point into the cycling stream back pressure and eddy zones may form resulting in insufficient mixing of the reactants. Moreover, sometimes these reactants will remain too long in a given zone and concentrations of one or the other may build up beyond that desired. This can result in local overheating and undesired heat accumulation.

Moreover, even a slight clogging or impedance of the nozzle openings exerts a great influence on the flow pattern in the main stream. The incoming jet is deflected or becomes unsymmetrical resulting in irregular or uneven mixing. Obviously such variations have an unfavorable and undesirable effect on the progress of the desired reaction.

The particular process referred to will produce lactams which are used in subsequent polymerization. However, it is essential that the purity of the lactam be very great in order that the polymerization be properly carried out.

The purity of the lactam is indicated by the melting point, the permanganate index (PZ), the volatile base index (FBZ) and the so-called APHA index. P2 is the time in seconds required to decolor 1 ml. of an n/ KMnO, solution, admixed to 100 ml. of a 1 percent aqueous lactam solution, to the hue of an equal quantity of reference solution. The reference solution is produced by dissolving 3 g. of CoCl 6H O and 2 g. of CuSO 5H O in l l. of water. The FBZ is determined by distilling from a solution of 20 g. of lactam in 200 ml. of In NaOH, 100 ml. of water into a receiver charged with n/lO acid. The consumption of n/lO acid determined by back titration and equivalent to the bases distilled over, in milliliter, represents the volatile base index. The APHA index is determined by comparison of a 40 percent aqueous lactam solution with the dilution series of a standard solution. The standard solution contains 1.245 g. of chlorplatinate K PtCl and l g. of cobalt chloride in l l. of water and corresponds to 500 APHA units.

The following table is a comparison of the aforementioned indices, between caprolactam produced by the process described herein under good mixing conditions and poor mixing conditions Good Mixing Conditions Poor Mixing Conditions In order to. overcome the deficiencies of prior art devices the present invention constitutes a mixing device of simple design which makes it possible to adapt the cross section of the flow of the feed liquid to the desired mixing conditions without the necessity of control valves at the feed points. The device will be best understood by reference to the accompany drawing constituting a part hereof and in which like reference characters indicate like parts.

The single FIGURE is a cross section device.

Pipe 1 is provided with bore 2 through which the process liquid flows. As shown in the Figure, the flow is fromright to left. Bore 2 is provided with a downstream portion 12 which flares out at a first angle B with the axis of the bore. In addition, in the preferred form of the invention the upstream side of the bore also flares providing a Venturi effect in the process liquid stream.

Throat l0 constitutes a constriction in bore 2 at which feed nozzles 7 are located. Nozzles 7 open into bore 2 at openings 8 and connect at their other end with annular chamber 6. The feed liquid is introduced into chamber 6 and is jetted into the main stream of the process liquid at a velocity of at least twice the velocity of the process liquid stream and preferably up to fifteen times the velocity of the process liquid stream. Nozzles 7 are generally cylindrical in cross section and the axis of the cylinder is arranged at a second angle A with the axis of the bore upstream of nozzles 7.

Angle A (the second angle) is from 30-90 and is preferably between 30 and 75. Angle B the first angle) is up to about l5and preferably from 3 to 15.

In order to provide greater flexibility in use of the device a closure is provided on each nozzle 7. The closure consists of conical tip 5 which is complementary in shape to nozzle 7. Tip 5 is mounted on valve stem 4 which in turn is threaded into valve body 3. Rotation of valve stem 4 in one direction causes conical tip 5 to advance from the open position (shown in the upper portion of the Figure) to the closed position (shown in the lower portion of the Figure). Of course, the rate of flow of feed liquid can be controlled by a suitable adjustment of the positron of conical tip 5 relative to nozzle 7.

of the improved The feed liquid is supplied to annular chamber 6 via inlet 13 which is connected to a source of pressure in order to cause the desired flow of feed liquid.

The device as described herein has no stagnant areas of liquid flow and desired thorough and intimate mixing is possible without the necessity of developing any turbulence or flow eddies. Moreover, in the preferred form of the device, the nozzles are easy to clean should they begin to clog simply by advancing the conical tips into nozzles 7 whereby any encrustations are cleared. This cleaning can be carried out without the necessity of shutting down the apparatus or interrupting the flow for more than a fraction of a second.

Moreover, it is possibly to vary the proportion of feed liquid to process liquid over an extremely wide range while still continuing to obtain a uniform and thorough mixture. As a result of the excellent mixing obtained with the present device, virtually no deviation from the desired optimum reaction temperature is noted. It will be appreciated that in prior art devices, due to local variations in concentration, overheating takes place and the optimum reaction temperature cannot be maintained.

While the device has been described particularly with respect to the continuous production of lactams from corresponding cyclic oximes, by additions of acid or oximes to the cycling rearrangement product, it can of course be used wherever it is desired to mix two liquid products where the mainstream is in laminar flow. These requirements are quite often found in neutralization reactions and the like.

What we claim is:

1. Apparatus for admixture of a feed liquid to a process liquid at least one of which is of high viscosity, comprising a pipe having a generally cylindrical bore, said process liquid flowing in said pipe, a throat in said bore, a portion of said bore downstream of and adjacent to said throat being wider than said throat and forming a first angle between said portion and the axis of said bore up to about 15, a plurality of feed nozzles for injection of said feed liquid disposed in said pipe, said nozzles being positioned around the periphery of said pipe and extending between a source of said feed liquid and said bore, said nozzles opening into said bore at said throat and being generally cylindrical in cross section, the axis of any of said nozzles forming a second angle with a portion of the axis of said bore upstream of said nozzle of between 30 to 75, whereby said feed liquid is injected through said nozzles and mixed with said process liquid, the axes of all said nozzles crossing the centerline of said bore at a point adjacent the downstream end of said throat, a releasable and adjustable nozzle closure associated with each nozzle, said closure having a tip complimentary in shape to said nozzle adapted to extend completely through said nozzle and into said pipe in closed position for scraping the wall of the noule clean when the said closure is in closed position.

2. Apparatus according to claim 1 wherein at least some of said closures are selectively closed during operation of the apparatus to prevent gumming of all of the nozzles and to assure continued clean operation of the apparatus. I

3. Apparatus according to claim 1 wherein said source of feed liquid comprises an annular chamber in said pipe and adjacent said throat.

4. Apparatus according to claim 1, wherein said first angle is 3 to 15.

5. Apparatus according to claim 1, wherein said second angle is 30 to 75.

6. Apparatus according to claim 1, wherein said tip has means for advancing into said nozzle and retracting away from said nozzle whereby said nozzle can be opened and closed.

7. Apparatus according to claim 1, wherein there is provided means for injecting said feed liquid at a velocity greater than twice the velocity of said process liquid.

8. Apparatus according to claim 1, wherein there is provided means for injecting said feed liquid at a velocity of from 2 to 15 times the velocity of said rocess li uid.

9. A method for admixture of eed liqui to a process liquid comprising flowing said process liquid along a predetermined substantially straight path, providing a throat in said path, providing a widening portion of said path downstream of said throat, providing a plurality of entrance paths for said feed liquid into said process liquid and selectively feeding said feed liquid through less than all of said entrance paths into said process liquid at said throat at an entry angle of 30 to to the upstream portion of said process liquid, said feed liquid being injected at a velocity of at least twice the velocity of said process liquid, said process liquid and said feed liquid forming a stream downstream of said throat, permitting said stream to widen at an exit angle of up to about 15 with the center line of said process liquid.

10. A method according to claim 9, wherein said exit angle is from 3 to 15.

11. A method according to claim 9, wherein the velocity of said feed liquid is from 2 to 15 times the velocity of said process liquid.

12. A method according to claim 9, wherein said entry angle is from 30 to 75. 

1. Apparatus for admixture of a feed liquid to a process liquid at least one of which is of high viscosity, comprising a pipe having a generally cylindrical bore, said process liquid flowing in said pipe, a throat in said bore, a portion of said bore downstream of and adjacent to said throat being wideR than said throat and forming a first angle between said portion and the axis of said bore up to about 15*, a plurality of feed nozzles for injection of said feed liquid disposed in said pipe, said nozzles being positioned around the periphery of said pipe and extending between a source of said feed liquid and said bore, said nozzles opening into said bore at said throat and being generally cylindrical in cross section, the axis of any of said nozzles forming a second angle with a portion of the axis of said bore upstream of said nozzle of between 30* to 75*, whereby said feed liquid is injected through said nozzles and mixed with said process liquid, the axes of all said nozzles crossing the centerline of said bore at a point adjacent the downstream end of said throat, a releasable and adjustable nozzle closure associated with each nozzle, said closure having a tip complimentary in shape to said nozzle adapted to extend completely through said nozzle and into said pipe in closed position for scraping the wall of the nozzle clean when the said closure is in closed position.
 2. Apparatus according to claim 1 wherein at least some of said closures are selectively closed during operation of the apparatus to prevent gumming of all of the nozzles and to assure continued clean operation of the apparatus.
 3. Apparatus according to claim 1 wherein said source of feed liquid comprises an annular chamber in said pipe and adjacent said throat.
 4. Apparatus according to claim 1, wherein said first angle is 3* to 15*.
 5. Apparatus according to claim 1, wherein said second angle is 30* to 75*.
 6. Apparatus according to claim 1, wherein said tip has means for advancing into said nozzle and retracting away from said nozzle whereby said nozzle can be opened and closed.
 7. Apparatus according to claim 1, wherein there is provided means for injecting said feed liquid at a velocity greater than twice the velocity of said process liquid.
 8. Apparatus according to claim 1, wherein there is provided means for injecting said feed liquid at a velocity of from 2 to 15 times the velocity of said process liquid.
 9. A method for admixture of feed liquid to a process liquid comprising flowing said process liquid along a predetermined substantially straight path, providing a throat in said path, providing a widening portion of said path downstream of said throat, providing a plurality of entrance paths for said feed liquid into said process liquid and selectively feeding said feed liquid through less than all of said entrance paths into said process liquid at said throat at an entry angle of 30* to 90* to the upstream portion of said process liquid, said feed liquid being injected at a velocity of at least twice the velocity of said process liquid, said process liquid and said feed liquid forming a stream downstream of said throat, permitting said stream to widen at an exit angle of up to about 15* with the center line of said process liquid.
 10. A method according to claim 9, wherein said exit angle is from 3* to 15*.
 11. A method according to claim 9, wherein the velocity of said feed liquid is from 2 to 15 times the velocity of said process liquid.
 12. A method according to claim 9, wherein said entry angle is from 30* to 75*. 